Pseudomonas aeruginosa (PA) is a malicious opportunistic pathogen both in terms of the severity and the outcome of infections it causes. A significant proportion of patients with cystic fibrosis (CF) are colonized at an early age (<1yr.), and most ultimately succumbto a chronic pulmonary infection from PA that is mostly present in the form of biofilms in the lungs of these victims. Additionally, the myriad of virulence determinants, including colonization factors and toxins that PA produces contribute to its pathogenic potential. Unfortunately, the exact contribution of these factors, alone or in combination, to even the simplest kind of PA infection has not yet been elucidated. This, organism is also highly resistant to most of the extant antimicrobial agents that are used to treat gram-negative infections. Expression of all the identified major virulence determinants in this organism is regulated by a variety of environmental conditions including the availability of iron. In fact, the dynamic control of intracellular iron concentrations is paramount to all biological systems. One aspect of this issue is that, especially in an aerobic environment, biologically useful iron (i.e. Fe2+)_Ls^xtremely_Iimiting_orJtJs-highly-inso^ evolved efficient mechanisms to acquire this nutrient from the insoluble form, which is generally in plentiful quantities. On the other hand, further acquisition of iron above biologically useful concentrations can have dire consequences for a cell (e.g P. aeruginosa). Excess free iron will catalyze the generation of highly reactive oxygen and nitrogen intermediates that will damage all known biological macromolecules. This conflict, in a major way is dealt with in a diverse array of pathogenic and commensal prokaryotic microbes, by represser proteins, which play the key role in controlling iron homeostasis at the level of transcription. The ferric uptake regulator (Fur) serves this function in many bacteria. In fact, in the opportunistic pathogen P. aeruginosa Fur (PA-Fur) is an essential protein that controls the expression of genes involved in the acquisition of environmental iron, including those that contribute to its virulence. More recently we also identified two PA-Fur regulated sRNAs transcripts we propose play a key role in the physiology of P. aeruginosa under iron replete conditions and inthe expression of quorum sensing compounds (quinolones - PQS), that are known to have a prominent impact on its virulence. This project will investigate the role of PA- Fur, and these PA-Fur regulated sRNAs, in the regulation of the expression of virulence factors (novel iron acquisition systems), in the physiology of intermediary metabolism controlled by the sRNA, the availability of PQS intermediates and the processes that are key to development of biofilms by PA during infections. One of our ultimate goals is to provide worthwhile information that would contribute to the development of novel antimicrobial agents for the treatment of P. aeruginosa infections.